Topic 6: Homeostasis Flashcards
Describe the principle of feedback loops
An external stimulus influence the variable –> receptors sense the changes in variable –> control center compare to the set-points –> make adjustment to the variable to return to normal
How does glucose get into the cell?
Through facilitated diffusion by transporters
Which organs are involved in controlling glucose and which one is the most important, why?
Muscles, liver, and fat are involved in controlling glucose level.
Liver is the most important one because it is the only one actually making glucose.
What is the role of diffusion in blood glucose levels?
Diffusion helps to dampen changes in blood glucose level and keep it close to the set points.
Name 2 types of transporters involved in glucose diffusion
SGLT: move glucose and sodium
GLUT: move glucose
Describe the role of SGLT
SGLT is important in:
- small intestines: diffuse glucose from guts into body
- kidney: restore glucose + sodium from urine back to the blood
Describe the role of GLUT and indicate which variation is located in muscle, fat, and liver
GLUT is responsible for glucose uptake in muscles, liver, and fat cells.
GLUT4: muscles, fat
GLUT2: liver
How is glucose stored and released in muscle cells?
Via diffusion, glucose gets into muscle cells, be metabolised, turned into pyruvate, and then stored as glycogen.
2 releasing ways:
- aerobic pathways: glycogen turned back into pyruvate
- anaerobic pathways: producing lactate
What happens to muscle cells after extreme period of fasting?
Muscles will break itself down into amino acids which are then used by liver to produce glucose.
How is glucose stored and released in fat cells?
Via diffusion, glucose gets into the cells, turned into glycerol 3-phosphate which combines with fatty acids to make triglycerides.
During fasting, triglycerides are turned into fatty acids and glycerol which enter the bloodstream and used by liver.
How is glucose stored and released in liver cells?
Glucose is turned into glycogen to be stored.
Liver can (thanks to GLUT2) reverse the storing process to make and release glucose. By-products of muscle and fat cells like amino acids, glycerol, lactate are used to produce pyruvate needed in the process of making glucose.
What are needed to control the process of storing and releasing glucose?
Glucose storage and release are controlled by hormonal control mechanism including insulin and glucagon.
What cells does Insulin target and how does it work?
Insulin targets muscle, fat, and liver cells.
In muscle and fat cells, insulin acts on GLUT4 to increase the number of transporters present in the membrane (in resting state, the number is low) –> control the diffusion
In liver cells, GLUT2 is present all the time, so insulin actually accelerates the production of glycogen.
What cells does Glucagon target and how does it work?
Glucagon targets liver cells and accelerates the production of glucose to release.
Why is glucose important?
Glucose is the main energy source for brain. This organ cannot store much glycogen, so it totally depends on the circulating blood glucose.
–> if glucose goes low, brain is the first one to be impacts.
